1. Field of the Invention
The present invention relates to a method of forming a water-repellent metal oxide film coated on a glass substrate by a sol-gel method using a solution of a metal alkoxide or acetylacetonate.
2. Description of the Prior Art
It is well known to coat a glass plate surface with a hard and abrasion-resistant film of a metal oxide such as silicon oxide. The metal oxide film can be formed, for example, by a sol-gel method using a solution of an organic metal compound such as a metal alkoxide or acetylacetonate. When the film-coated glass plate is used, for example, as a vehicular window glass, it is desired that the film be repellent to water.
JP-A (Patent) 64-68477 discloses a method of forming a water-repellent metal oxide film coated on a steel sheet. In this method, first, at least 0.005 wt % of at least one organic metal compound selected from the group consisting of simple alkoxides having no organic group other than alkoxyl group, monomethyl alkoxides and acetylacetonate of Al, Zr, Ti, Si, W, Ce, Sn and Y, and fluoroalkylsilane amounting to 0.005 to 0.30 mol % of the organic metal compound, are dissolved in an alcohol solution. Then, the sheet is coated with the solution. Then, the coated sheet is heated at a temperature not lower than 100.degree. C., thereby forming a metal oxide film which has water repellency. However, this method has the following drawback.
When this method is used to form a metal oxide film coated on a glass plate, water repellency of this film does not last for a long period in the outdoors due to elution of alkali metal ions from the glass plate.
JP-A (Patent) 1-126244 discloses a method of forming a water-repellent film coated on a glass plate. In this method using a dip coating, first, the glass plate is dipped in a solution consisting of polydimethylsiloxane and a hydrocarbon which takes the form of liquid at room temperature. Then, the glass plate is pulled up, and heated at a temperature in the range from 250.degree. to 300.degree. C. for 10 to 30 min, thereby forming a film which has water repellency on the glass plate. However, this method has the following drawback.
Water repellency of this film is impaired in the outdoors in a relatively short time due to an insufficient thickness of the film.